1. Field of the Invention
This invention relates to an improved clutch facing, and more particularly to a method for manufacturing a clutch facing of the type used for automobiles and the like.
2. Description of the Prior Art
Clutch facings are usually made of an inorganic fiber-based friction material which include many different types. Recently, the clutch facing used for automobiles and the like is made by a so-called spiral woven system because the clutch facing made by this system is preferable with respect to performance or durability.
The important qualities in a clutch facing are durability against wear, a desirable friction coefficient, high resistance against shudder and so on, but it is well known that the durability against wear is inconsistent with resistance against shudder. Therefore, a problem exists in clutch facings with regard to needed offsetting of these contradictory properties. The term "durability against wear" means durability determined by the rate of wear, and the term "resistance against shudder" refers to vibration of a vehicle body caused when the vehicle starts and may be demonstrated by acceleration G of the vehicle.
Conventional clutch facings produced by the spiral woven system are, as will be explained hereinbelow, obtained through various processes including mixing relatively long asbestos fiber with lubricant, organic fiber and so on, then making an asbestos fiber string with a fine brass core, soaking the asbestos in a binder agent such as thermosetting phenolic resin, forming the asbestos fiber string into a loop shape under pressure, then heating the loop-shaped string so as to cure perfectly and finally smoothing the surface of loop-shaped string with a grinding machine, thereby obtaining the complete clutch facing. Upon forming under pressure, a plurality of radial slits are provided on the friction surface of some clutch facings. The effect of such slits is to improve the engagement of the flywheel or pressure plate by the clutch facing and the adhesion thereto upon clutch releasing.
Contradiction in two properties as mentioned above is caused by the rate of a binder agent for the asbestos fiber string, that is, the rate of the resin such as phenolic resin and harness of the clutch facing after pressure forming. Namely, as well known, the higher the rate of the resin or the hardness is, the better the durability against wear is, while the resistance against shudder becomes progressively worse. The clutch facings of a high rate of resin and a high degree of hardness are being supplied in the market for use with a result of insufficient resistance against shudder. The term "high hardness" or "low hardness" means a Rockwell hardness on the Moh scale (HRM), with the former term meaning hardness of a range greater than 60 the latter meaning a hardness of a range less than 60. The term "high rate of resin" means that the rate of the binder agent is more than 25 weight percent for every 100 weight percent asbestos fiber string. The term "low rate of resin" means that the rate of the binder agent is 14-24 weight percents for every 100 weight percent of asbestos fiber string.